Over voltage and over current protection integrated circuit

ABSTRACT

An integrated circuit is disclosed including a primary input for receiving an input voltage, a battery voltage input for receiving a battery voltage signal and an output for providing an output voltage higher than the battery voltage. First circuitry responsive to the input voltage is provided for turning off the output voltage responsive to an input over voltage condition. Second circuitry responsive to the battery voltage signal is provided for turning off the output voltage responsive to a battery over voltage condition. Third circuitry provides for over current protection.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of United States Provisional ApplicationSerial No. 60/576,865, filed on Jun. 3, 2004, entitled OVER VOLTAGE ANDOVER CURRENT PROTECTION INTEGRATED CIRCUIT.

TECHNICAL FIELD OF THE INVENTION

The present invention relates in general to over voltage and overcurrent protection circuits, and more particularly, to a singleintegrated circuit containing both over current and over voltageprotection for use in conjunction with other circuitry to provideredundant protection.

BACKGROUND OF THE INVENTION

Many systems, such as battery charging systems, require both overvoltage and over current protection in order to prevent damage toelectronic components included within a system such as a batterycharging system. To date, protections from input over voltage, batteryover voltage and charge current over current have required the use ofthree separate circuits and/or chips in order to protect a system fromthese over voltage and over current conditions. This is especially sowith respect to Li-ion batteries. A Li-ion rechargeable battery is verysensitive to over charge. Over charging a Li-ion battery may lead toexplosion, flame or other hazardous situations. A charging system needsto charge the battery to a high precision final voltage so that thebattery is not over charged, neither under charged. From safety point ofview, it is very critical that the Li-ion battery is properly protectedagainst over charge. Over charge is typically a result of failures in acharging system. A charging system typically consists of an ac/dcconverter (typically named a wall adapter or an ac adapter) and acharging circuit that provides precision current limit and precisionfinal battery voltage. An over-charge protection function is typicallyresiding in a Li-ion battery pack to protect the battery againstcharging system failures. However, some unqualified after-market batterypacks do not have the protection function built-in, which greatlyincreases the risk of explosion, flame, or other hazardous situationswhen a single failure occurs in the charging system. When any of theabove events occurs, the manufacture of the handheld device will beliable to any resulted damage.

The use of multiple chips for providing these protections requires agreat deal of space within an electronic device, including threeseparate chips for providing the protections. Thus, there is a need fora chip for providing an electronic device with multiple types of overvoltage and over current protection in order to save space within theelectronic device requiring such over voltage and over currentprotection.

SUMMARY OF THE INVENTION

The present invention, disclosed and claimed herein, in one aspectthereof, comprises an integrated circuit including a primary input forreceiving an input voltage, a battery voltage input for receiving abattery voltage signal and an output for providing an output voltagehigher than the battery voltage. First circuitry responsive to the inputvoltage is provided for turning off the output voltage responsive to aninput over voltage condition. Second circuitry responsive to the batteryvoltage signal is provided for turning off the output voltage responsiveto a battery over voltage condition.

In another aspect of the present invention, there is also provided overcurrent protection.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is now made to the following descriptiontaken in conjunction with the accompanying Drawings in which:

FIG. 1 is a block diagram of an integrated circuit providing both overvoltage and over current protection;

FIG. 2 is a block diagram illustrating an application of the circuit ofFIG. 1 with a battery charger;

FIG. 3 is a timing diagram for the gate voltage of the power FET of thecircuit of FIG. 1;

FIG. 4 illustrates the operation regions of a battery charger output andthe integrated circuit of FIG. 1 output;

FIG. 5 is a basic functional block diagram of a charging system; and

FIG. 6 illustrates a hand-held application of the integrated circuit.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly to FIG. 1, there isillustrated an over voltage, over current and overcharge protection IC100. The over voltage and over current protection IC 100 is optimizedfor the safety of a battery charging system in, for example, a hand heldsystem that utilizes a Lithium Ion battery which must be operated in asafe region in order to ensure that the battery does not catch fire orexplode. The IC 100 protects three possible failure mechanisms in acharging system: input over voltage (the voltage input to the overallsystem), battery over voltage and charge current over current. When anyof the above three failure mechanisms occur, the IC 100 turns off aninternal p-channel MOSFET 102 to remove power from the charging system.Together with a battery charger IC (not shown) and a protection modulein a battery pack, the charging system has triple level protection tolimit the battery cell voltage in a safe region.

The input over voltage protection (OVP) threshold is set to 6.5Vinternally, but may be adjusted to other values easily using a metalspin. When the input voltage exceeds the programmed threshold, the IC100 turns off the PFET 102 in less than 1 μs to prevent the high voltageinput from damaging the electronics in a handheld system. The IC 100 isdesigned to withstand up to 30V of input voltage. The current in thePFET 102 is over current protected and the threshold is programmablewith an external signal resistor up to 1.5 A. The over currentprotection (OCP) has a built-in delay to prevent false triggering. Thebattery OVP is realized through a battery voltage monitoring pin VB 104.The battery OVP threshold is set at 4.4V and a built-in 100 μs blankingtime avoids mistakenly triggering the OVP by any transient voltage. Allcomparators in the integrated circuit 100 have hysteresis to preventoscillation as the voltages are moving across the thresholds. The FETdriver 106 is designed to turn on the internal PFET 102 slowly to avoidinrush currents at power up but will turn off the PFET 102 quickly inorder to remove power before any damage occurs to a circuit. The IC 100also includes a control input 108 to allow other logic circuits 110 toturn off the PFET 102.

The PFET 102 has a gate that is controlled in order to control the gatevoltage, V_(GS), thereof. The V_(GS) that is required to turn the PFET102 on may be less than the full input voltage such that the gatevoltage required to turn on the transistor is not necessarily groundand, therefore, the FET driver 106 is operable to lower the V_(GS)voltage to a level sufficient to turn it on and with a profile thatprovides a relatively slow turn on in order to prevent a large inrush ofcurrent. Further, as will be described herein below, over currentprotection is inhibited until the PFET 102 is sufficiently turned on.Therefore, there is a control signal generated on a line 107 input tothe logic block 110 that is operable to detect when the voltage V_(GS)is large enough to sufficiently turn on the transistor in order toenable over current protection. When the voltage is at such a level,then the line 107 has a voltage disposed thereon indicating a thresholdhas been passed and will provide a logic signal to logic block 110.

The input pin VIN 112 provides a connection for the input power source.The VIN pin 112 is designed to withstand up to a 30V input. Input pin112 is applied to a first node 114, which is connected to the input ofthe POR pre-reg ref 116. The POR pre-reg ref contains power on reset,pre-regulator and voltage references, which voltage references areprovided with a band gap voltage generator, a temperature and voltagestable device. The power-on-reset prevents operation when the inputvoltage is below 2.5V. The pre-regulator outputs the power supplyvoltage for the control circuits. The reference generates the 1.2V bandgap voltage, which is applied to a number of the comparators. The poweron reset (POR) provides a POR threshold of 2.5V with a built-inhysteresis of 100 mV. Before the input voltage reaches the PORthreshold, the power PFET 102 is off. Once the input voltage VIN exceedsthe POR threshold, the IC 100 resets itself and starts to slowly turn onthe power PFET 102. The slow turning on reduces the inrush current aswell as the voltage drop during the transition. The input voltage VINand the output voltage are monitored whenever the input is above the PORthreshold, but the current is monitored only after the power PFET 102 isfully turned on, indicated by the voltage on the power PFET 102 gate andthe signal on line 107.

Node 114 also applies an input to the FET driver 106. The FET driver 106turns on the power PFET 102 slowly but turns off the power PFET quicklyto avoid damage to the internal circuitry of an attached electronicdevice. The FET driver 106 is also connected to receive an input fromlogic circuit 110 and provides an input to logic circuit 110.

Node 114 also is connected to a resistor divider network consisting of aresistor R1 118 and a resistor R2 120 connected to the positive input ofa comparator 122. The comparator 122 is the comparator for the inputover voltage protection. The resistors 118 and 120 set the threshold forinput over voltage protection. The input voltage applied at the VIN pin112 is monitored by the comparator 122. Comparator 122 has an accuratereference of 1.2V from the band gap reference generated by the PORpre-reg ref 116. The over voltage protection threshold is set by theresistor divider network consisting of resistor 118 and resistor 120.The initial threshold is set to 6.7V. Metal options enable the thresholdto be adjusted between 5.5V and 6.7V. The overall accuracy is betterthan three percent (3%) over the entire recommended operatingconditions. When the input voltage exceeds the threshold, the comparatoroutputs a logic signal to the logic circuitry 110 to turn off the powerFET 102 within 1 μs to prevent the input voltage from damaging theelectronics in the associated system.

The FET driver 106 provides an output to the gates of power PFET 102 andsensor PFET 103. The drain/source path of power FET 102 has a diode 124connected in parallel therewith with the cathode connected to node 114.This diode is the parasitic body diode that comes with the FET. Thesource of power FET 102 is connected to an output pin 126. The source ofpower transistor 102 is also connected to the negative input of acomparator 128. The positive input of a comparator 128 is connected tothe source of sensor transistor 103. Comparator 128 is the over currentprotection comparator. Transistor 102 and transistor 103 have a sizeratio of approximately 200:1. The over current protection (OCP)threshold is 200 times the current in transistor 103. Over currentprotection is disabled before the power FET 102 is fully turned on. Thecurrent in the power FET 102 is limited to prevent charging the batterywith an excessive current. The current is sensed using the voltage dropacross the power FET 102 after the power FET 102 is turned on. Thereference of the over current protection is generated using the sensortransistor 103. The current in the sensor transistor 103 is forced tothe value programmed by the ILIM pin 130 and an external VRLIM resistor206. The ILIM pin 130 is the over current protection threshold settingpin. By connecting the resistor 206 between the ILIM pin 130 and ground(or some appropriate reference voltage), the over current protectionthreshold may be established. The size of the power PFET 102 is 200times that of the sensor transistor 103; therefore, when the current inthe power PFET 102 is 200 times of the current in the sensing FET 103,the drain voltage of the power FET 102 falls below that of the sensingFET 103. The comparator 128 then outputs a signal to the logic circuit110 to turn off the power FET 102.

In order to define the current to sensor transistor 103, a currentsource is provided. This current source is provided in the form of atransistor 125 having the source/drain path thereof connected betweenthe source/drain of transistor 103 and the ILIM input pin on one side ofresistor 206. The gate of transistor 125 is connected to the output of aunity gate amplifier 127, the negative input thereof connected to theILIM pin 130 and the positive input thereof connected to a node 129.This is driven by a 1.2V stable reference voltage. The amplifier 127 andtransistor Q3, when connected on one side of the source/drain path tothe node 130 on the ILIM pin 130, constitutes a current source. The 1.2Vreference voltage, since it is stable, is reflected on the node 130 andthe value of the resistor 206 defines the current there through. Thus,the current through transistor 103 is defined by the current throughtransistor 125. The current through transistor 103 will result in aknown and fixed voltage drop, since there is a finite R_(DSON). This isa temperature varying resistance. Similarly, transistor 102 has anR_(DSON) that is significantly smaller than the R_(DSON) of transistor103, by a factor of approximately 200. However, it could be any number.Since the R_(DSON) of both transistors varies with respectivetemperature, they will track each other over temperature. Thus, in orderto detect whether the current through transistor 102 has increased abovea predetermined threshold, which is above the current required toincrease the voltage across R_(DSON) of transistor 102 greater than thevoltage across R_(DSON) of transistor 103, the comparator 120 willdetect such and output a signal indicative of this to the logic circuit110.

The battery over voltage protection is realized with the VB pin 104.Comparator 134 monitors the VB pin 104 and issues an over voltage signalwhen the battery voltage exceeds a 4.4V (+ or −75 mV) battery overvoltage protection (OVP) threshold. The battery voltage is appliedthrough a buffer 136 that is used to minimize the load current from thebattery. The current is a leakage current from the battery. The buffer136 is designed so that no current is flowing out of the VB pin 104 evenunder failure modes. An external series 1 MΩ resistor R_(OPT) (notshown) is required to minimize the current from the VB pin 104 to thebattery under failure modes, which further enhance the safety of thecharging system. Resistors R3 138 and R4 140 set the over voltageprotection threshold at 4.4V for the battery. The threshold has a 150 mVbuilt in hysteresis. Thus, the battery voltage has to come back to 4.25Vbefore the battery over voltage signal is cleared. When comparator 134indicates the over voltage, the power PFET 102 is turned off within 1μs. The control logic 110 contains a counter that if the battery overvoltage or over current (described above) event occurs sixteen times,the battery over voltage or the over current indication is latched andthe power PFET 102 is turned off permanently, unless the IC 100 ispowered down and then up again. Comparator 134 has a built-in 100 μsblanking time to prevent any transient voltage from triggering the overvoltage protection. It is noted that the start-up is a “soft start” thatrequires a certain period of time for the turn-on of the transistor 102in order to prevent any inrush current, in the event that the overcurrent indication was faulty. Therefore, there will be slow turn-onand, if a determination of default still exists and a fast turn-off willthen occur. This cycle will continue sixteen times. The length of timefor each cycle is a function of the amount of time required to turn thetransistor 102 on and to turn it off and for the sensing operations.

The leakage current flowing into or out of the VB pin 104 is minimized.This has two purposes. It first minimizes loading to the battery when anAC adaptor is not plugged in. Additionally, this allows the optionalresistor R_(OPT) of a 1 MΩ magnitude to be inserted between the VB pin104 and the battery so that if the IC fails, the current to the batteryis limited. When a 1 MΩ resistor is used, even a voltage level of 30V atthe VB pin 104 can only result in a 30 μA current output, which can beeasily absorbed by the leakage current of other devices connected to thebattery. To minimize the leakage current, a buffer is usually needed atthe VB pin.

Metal options are required to adjust the center of the over voltageprotection threshold within a +/−50 mV range of the 4.4V threshold.

The IC 100 has a control pin 108 used either as a control input or as anindication input. This is input to the gate of a transistor 109, havingthe source/drain path connected between ground and a control input tologic circuit 110. The control input allows other logic circuits to turnoff the PFET 102. When the control pin 108 is driven to a logical highlevel, the power PFET 102 will be turned off. Driving the control pin108 low or leaving it floating turns on the PFET 102. This pin 108 withthe internal 200 kΩ pull-down transistor 109 is compatible with 1.8Vlogic.

The WRN pin 142 is an open-drain output that indicates a LOW signal whenany of the three over current or over voltage protection conditionsoccur. This allows the microprocessor to give an indication to the userto further enhance the safety of the charging system. The WRN pin isconnected to a transistor 144 having the gate thereof connected to thelogic circuit 110.

The FET driver 106, as described herein above, is designed to turn onthe power PFET 102 slowly to avoid inrush current at power up but willturn off the power PFET 102 quickly in order to remove the power beforeany damage occurs. FIG. 3 illustrates the timing diagram for drawing thegate voltage thereof. The initial gate voltage is zero voltage. When thegate voltage starts to turn on the power FET 102, the gate voltageslowly drops. When the gate voltage reaches approximately −1V thresholdvoltage (referenced to the source of the FET), the PFET 102 starts toturn on. The over current protection circuit is not allowed to affectthe gate control until the gate voltage drops further to approximately−3V to ensure fully turning on the power FET 102. When the power FET 102needs to be turned off, the gate voltage is pulled to the source voltagewithin 1 μs. The asymmetrical speeds of turning on and off the power FET102 also creates delays for the 16 counts of battery over voltageprotection and/or over current protection events.

There are six inputs to the control logic block 110: the threecomparator outputs, the power-on-reset comparator output, the gatevoltage comparator output from the gate driver block, and the CTL logicinput. The gate voltage comparator output gates the OCP signal todisable the OCP functions when the power MOSFET is not fully turned on.The control logic 110 also contains a 4-bit counter for counting the OCPand battery OVP events. When both events reach 16 counts, the power FETis turned off permanently. All other five signals can turn off the powerFET 102. The control logic also has two output signals. One signal goesto the gate FET driver 106 to turn off the power FET 102 and the samesignal is used to drive the open drain WRN output. Note that the logicblock 110, as well as all other circuit elements on IC 100, are poweredby VIN.

Referring now to FIG. 2, there is illustrated a typical applicationcircuit using the over voltage protection and over current protection IC100 described herein above. The IC 100 has connected at its input adiode 202 and capacitor 204. The resistor R_(ILIM) 206 is connected tothe ILIM pin 130. By connecting the resistor R_(ILIM) 206 between theILIM pin 130 and ground, the over current protection threshold may beestablished. A battery charger 208 is connected to the output pin 126. Aresistor R_(OPT) 210 is connected between the VB pin 104 and the battery212 to protect from currents as described herein above.

Referring now to FIG. 4, there is illustrated a voltage specificationfor the operation of the combination of the IC chip 100 and the batterycharger 208. The battery charger 208 can be any type of battery chargerchip, one being the ISL 6292C, manufactured by Intersil. This is aconventional battery charger chip that outputs voltage and current andprovides internal protection thereto. There is provided a specifiedlimit to the battery charger operation, this is referred to by a dottedline 402 that defines the maximum current versus voltage, which can beseen to be flat at around 100 mA and a flat portion 404 and then risesto a level of approximately 250 mA at a voltage of 2.0V to a current of250 mA at a flat portion of the dotted line 406. At a voltage ofapproximately 2.5V, the battery charger is confined to a current ofapproximately 1,000 mA. At a voltage of 4.2V, the battery voltage, aportion of a dotted line 408 limits the voltage. The battery charger 208is designed such that it will limit the current to a current of lessthan 100 mA at a flat portion 410 and, at a voltage of approximately2.7V, would allow the current to rise to a level of approximately 750 mAat a limit 412. The charger outputs voltage is limited to 4.2V.Therefore, the charger can operate in two modes, a constant currentmode, which is typical on charging and, once it reaches a certainvoltage, it will then go into a constant voltage mode and the currentwill reduce. However, the portion 410 and the portion 412 define thelimits as to the amount of current versus voltage that the charger canprovide as an output. Therefore, when an over-voltage condition occurs,the current will be shut down to “0”. When the current reaches a limitabove 750 mA, this current will be limited. The logic chip 110 providesa limit of 1,000 mA for all voltages such that, in the event of afailure of the battery charger 208, the current cannot exceed thatlimit, i.e., if the current through the transistor 102 exceeds thatlimit, it will turn off. The voltage battery is limited to 4.4V, afterwhich current will be shut down to a value of “0.” There is provided anoutside boundary dotted line 416, which represents the absolute maximumcurrent and voltage that the battery can operate on. Current above thisat voltages above those associated with the line 416 could result indamage to the battery or even fire. Therefore, any current limiting mustbe maintained below that.

A complete charging system is illustrated in FIG. 5, including an ACadaptor 502, the over voltage and over current protection IC 100, abattery charger 504, and a battery pack 506. Each of these units withinthe system are capable of failure. When any two of the blocks fail, thefollowing consequences will occur. When the AC adaptor 502 and theintegrated circuit 100 fail, the battery charger 504 will also fail, butthe protection module in the battery pack 506 will protect the batterycell. When the AC adaptor 502 and the battery charger 504 fail, both theintegrated circuit 100 and the battery pack 506 will protect the batterycells. When the AC adaptor 502 and the battery pack 506 fail, thebattery charger 504 will limit the battery voltage, and the IC 100provides an additional level of protection. When the IC 100 and thecharger 504 fail, the protection module in the battery pack 506 willprotect the battery cells. When the IC 100 fails and the battery pack506 fails, the battery charger 504 will limit the battery voltage to4.2V within a 1% error. Finally, when the battery charger 504 and thebattery pack 506 fail, the IC 100 will sense an over voltage case andremove power from the system. Thus, as can be seen, there is at leastanother level of protection available when any two blocks in the systemmay fail.

Referring now to FIG. 6, there is illustrated another application of theIC 110. In this application, there is a self-contained unit, such as ahand-held telephone or other appliance. This would include within acasing 602 various operating circuitry 604. This operating circuitry 604operates from a power supply line 606, which is connected to the top ofthe battery 202. Therefore, it operates on the voltage at the batterylevel. Therefore, it can be seen that the battery charger 208, whencharging, can charge the battery 202 and, if the battery charge state istoo low, can actually provide current for the operating circuitry whenan AC/DC supply source 608 is plugged into the VIN input 112 of the IC110. The IC 110, as noted herein above, isolates the pin 112 from theoutput pin 126 that drives the battery charger 208. It is possible, inan alternate embodiment (not shown), that the operating circuitry 604can operate, during charging, from the input to the battery charger 208.This would require switches internal to the circuit and regulators suchthat the voltage on line 606 were regulated. Typically, the operatingcircuitry 604 will have built-in regulation circuits such that thevoltage to the battery can be regulated to a fixed voltage for operatingthereon.

In summary, the system of the present disclosure offers a minimal system(a simple single chip) to provide a redundant protection againstfailures of the charging system, so that any single failures in thecharging system will not lead to over charging the Li-ion battery.Taking the protection function in the battery pack into account, thebattery is free from over charge when two failures happen in thecharging system simultaneously. Such redundant protection greatlyreduces the risk of over charging the Li-ion battery. In addition toprotecting the battery, this single chip in this invention also protectsother electronic components in the handheld device against over voltagefailure at the input.

Although the preferred embodiment has been described in detail, itshould be understood that various changes, substitutions and alterationscan be made therein without departing from the spirit and scope of theinvention as defined by the appended claims.

1. A protection circuit implemented on a single chip integrated circuitfor protecting a battery operating at a set operating voltage,comprising: a primary input on the single chip integrated circuit forreceiving an input voltage at a level above the set operating voltage;an output on the single chip integrated circuit for driving a voltagetranslating circuit that is operable to lower the input voltage level tothe set operating voltage level; an input over voltage protectioncircuit for detecting an input over voltage condition wherein the inputvoltage applied to the primary input exceeds a predetermined inputvoltage limit and generating an input over voltage control signalresponsive thereto; and a battery over voltage protection circuit fordetecting a battery over voltage condition wherein a battery inputvoltage applied to the battery exceeds the set operating voltage by apredetermined battery over voltage limit and generating a battery overvoltage control signal responsive thereto; a switch connecting saidprimary input to said output, wherein said switch is responsive to theinput over voltage control signal for controlling said switch todisconnect the primary input from the output when the input voltagelimit is exceeded by the input voltage and further wherein said switchis also responsive to the battery over voltage control signal forcontrolling said switch to disconnect the primary input from the outputwhen such battery over voltage limit is exceeded by the battery inputvoltage.
 2. The protection circuit of claim 1, and further comprising anover current circuit for detecting an over current condition where thecurrent through said switch exceeds a predetermined current limit andgenerating an over current control signal responsive thereto.
 3. Theprotection circuit of claim 1, wherein the voltage translating circuitcomprises a battery charger which has associated therewith internalprotection circuitry for protecting for an input over voltage conditionabove a predetermined voltage level and for protecting the battery froma battery over voltage condition.
 4. The protection circuit of claim 3,wherein the predetermined voltage of the battery charger is less thanthe input over voltage limit and the battery over voltage condition ofthe battery charger is less than battery over voltage limit.
 5. Theintegrated circuit of claim 1, wherein said input over voltageprotection circuit includes: a reference voltage generator forgenerating a known reference voltage; a comparator for comparing theinput voltage with the reference voltage and, if it exceeds thepredetermined relationship input voltage limit outputting an input overvoltage fault signal; and wherein the switch conducts between saidprimary input and said output in the absence of said input over voltagefault signal and being non conductive in the presence of said input overvoltage fault signal.
 6. The integrated circuit of claim 1, wherein saidbattery over voltage protection circuit includes: a reference voltagegenerator for generating a known reference voltage; a comparator forcomparing the battery input voltage with the reference voltage and, ifthe battery input voltage exceeds the predetermined battery over voltagelimit outputting a battery over voltage fault signal; and wherein theswitch conducts between said primary input and said output in theabsence of said battery over voltage fault signal and being nonconductive in the presence of said battery over voltage fault signal. 7.The integrated circuit of claim 1, wherein the battery is a Lithium Ionbattery.
 8. A protection circuit implemented on a single chip integratedcircuit for protecting a battery operating at a set operating voltage,comprising: a primary input on the single chip integrated circuit forreceiving an input voltage at a level above the set operating voltage;an output on the single chip integrated circuit for driving a voltagetranslating circuit that is operable to lower the input voltage level tothe set operating voltage level; an input over voltage protectioncircuit for detecting an input over voltage condition wherein the inputvoltage applied to the primary input exceeds a predetermined inputvoltage limit and generating an input over voltage control signalresponsive thereto; and a battery over voltage protection circuit fordetecting a battery over voltage condition wherein a battery inputvoltage applied to the battery exceeds the set operating voltage by apredetermined battery over voltage limit and generating a battery overvoltage control signal responsive thereto; an over current circuit fordetecting an over current condition where the current through saidswitch exceeds a predetermined current limit and generating an overcurrent control signal responsive thereto; a switch connecting saidprimary input to said output, wherein said switch is responsive to theinput over voltage control signal for controlling said switch todisconnect the primary input from the output when the input voltagelimit is exceeded by the input voltage, wherein said switch is alsoresponsive to the battery over voltage control signal for controllingsaid switch to disconnect the primary input from the output when suchbattery over voltage limit is exceeded by the battery input voltage, andfurther wherein said switch is responsive to the over current controlsignal for controlling said switch to disconnect the primary input fromthe output when such current limit is exceeded by the current throughsaid switch.
 9. The protection circuit of claim 8, wherein the voltagetranslating circuit comprises a battery charger which has associatedtherewith internal protection circuitry for protecting for an input overvoltage condition above a predetermined voltage level and for protectingthe battery from a battery over voltage condition.
 10. The protectioncircuit of claim 8, wherein the predetermined voltage of the batterycharger is less than the input over voltage limit and the battery overvoltage condition of the battery charger is less than battery overvoltage limit.
 11. The integrated circuit of claim 8, wherein said inputover voltage protection circuit includes: a reference voltage generatorfor generating a known reference voltage; a comparator for comparing theinput voltage with the reference voltage and, if it exceeds thepredetermined relationship input voltage limit outputting an input overvoltage fault signal; and wherein the switch for conducts between saidprimary input and said output in the absence of said input over voltagefault signal and being non conductive in the presence of said input overvoltage fault signal.
 12. The integrated circuit of claim 8, whereinsaid battery over voltage protection circuit includes: a referencevoltage generator for generating a known reference voltage; a comparatorfor comparing the battery input voltage with the reference voltage and,if the battery input voltage exceeds the predetermined battery overvoltage limit outputting a battery over voltage fault signal; andwherein the switch for conducts between said primary input and saidoutput in the absence of said battery over voltage fault signal andbeing non conductive in the presence of said battery over voltage faultsignal.
 13. The integrated circuit of claim 8, wherein the battery is aLithium Ion battery.
 14. The protection circuit of claim 1, wherein theswitch is further responsive to the over current control signal forcontrolling said switch to disconnect the primary input from the outputwhen such current limit is exceeded by the current through said switch.